Real Estate Assets and Construction in Progress (Summary of Properties Owned or Leased by the Company) (Details) $ in Thousands	Mar. 31, 2019 USD ($) property	Dec. 31, 2018 USD ($) property
Real Estate Properties [Line Items]
Land	$ 105,541	$ 105,541
Buildings, Improvements and Equipment	2,031,825	1,917,251
Construction in progress	803,888	790,064
Total cost	2,941,254	2,812,856
Manassas, Virginia | Assets Held For Sale
Real Estate Properties [Line Items]
Construction in progress		71,000
Owned Properties | Atlanta, Georgia (Atlanta-Metro)
Real Estate Properties [Line Items]
Land	20,416	20,416
Buildings, Improvements and Equipment	497,111	493,446
Construction in progress	110,769	88,253
Total cost	628,296	602,115
Owned Properties | Irving Texas
Real Estate Properties [Line Items]
Land	8,606	8,606
Buildings, Improvements and Equipment	346,276	345,615
Construction in progress	104,988	99,445
Total cost	459,870	453,666
Owned Properties | Richmond, Virginia
Real Estate Properties [Line Items]
Land	2,180	2,180
Buildings, Improvements and Equipment	253,593	253,098
Construction in progress	68,059	67,932
Total cost	323,832	323,210
Owned Properties | Chicago, Illinois
Real Estate Properties [Line Items]
Land	9,400	9,400
Buildings, Improvements and Equipment	152,704	130,150
Construction in progress	120,999	133,095
Total cost	283,103	272,645
Owned Properties | Suwanee, Georgia (Atlanta-Suwanee)
Real Estate Properties [Line Items]
Land	3,521	3,521
Buildings, Improvements and Equipment	167,173	166,298
Construction in progress	2,977	3,188
Total cost	173,671	173,007
Owned Properties | Ashburn, Virginia
Real Estate Properties [Line Items]
Land	17,326	17,325
Buildings, Improvements and Equipment	95,585	63,245
Construction in progress	166,484	184,951
Total cost	279,395	265,521
Owned Properties | Piscataway New Jersey
Real Estate Properties [Line Items]
Land	7,466	7,466
Buildings, Improvements and Equipment	98,501	97,806
Construction in progress	34,141	33,472
Total cost	140,108	138,744
Owned Properties | Santa Clara, California
Real Estate Properties [Line Items]
Buildings, Improvements and Equipment	105,386	98,548
Construction in progress	1,250	7,600
Total cost	106,636	106,148
Owned Properties | Dulles, Virginia
Real Estate Properties [Line Items]
Land	3,154	3,154
Buildings, Improvements and Equipment	72,756	72,435
Construction in progress	4,018	3,852
Total cost	79,928	79,441
Owned Properties | Sacramento, California
Real Estate Properties [Line Items]
Land	1,481	1,481
Buildings, Improvements and Equipment	64,904	64,874
Construction in progress	91	92
Total cost	66,476	66,447
Owned Properties | Fort Worth, Texas
Real Estate Properties [Line Items]
Land	9,078	9,079
Buildings, Improvements and Equipment	18,619	18,623
Construction in progress	50,869	43,715
Total cost	78,566	71,417
Owned Properties | Princeton, New Jersey
Real Estate Properties [Line Items]
Land	20,700	20,700
Buildings, Improvements and Equipment	34,083	34,046
Construction in progress	424	431
Total cost	55,207	55,177
Owned Properties | Phoenix, Arizona
Real Estate Properties [Line Items]
Construction in progress	30,016	29,562
Total cost	30,016	29,562
Owned Properties | Hillsboro, Oregon
Real Estate Properties [Line Items]
Construction in progress	44,942	39,835
Total cost	44,942	39,835
Owned Properties | Manassas, Virginia
Real Estate Properties [Line Items]
Buildings, Improvements and Equipment	8
Construction in progress	54,245	45,194
Total cost	54,253	45,194
Owned Properties | Other
Real Estate Properties [Line Items]
Land	2,213	2,213
Buildings, Improvements and Equipment	35,795	35,720
Construction in progress	167	113
Total cost	$ 38,175	$ 38,046
Leased Properties
Real Estate Properties [Line Items]
Number of facilities leased | property	9	10
Leased Properties | Owned Properties
Real Estate Properties [Line Items]
Buildings, Improvements and Equipment	$ 89,331	$ 43,347
Construction in progress	9,449	9,334
Total cost	$ 98,780	$ 52,681